Researches on an organic thin-film light emitting device in which electrons injected from a cathode and holes injected from an anode emit light when they are recombined in an organic fluorescent body held by both electrodes have been actively conducted in recent years. This light emitting device is characteristic for high luminance light emission in the form of a thin type and under a low driving voltage, and multicolor light emission due to selection of a fluorescent material, and has been paid attention.
Such researches have undergone many studies for practical use since C. W. Tang et al. of Kodak Co., Ltd. showed that an organic thin-film device emits light at high luminance, and organic thin-film light emitting devices have steadily come into practical use as they have been employed in main displays of mobile phones, and the like. However, there are still many technical problems and, especially, attainment of both increased efficiency and prolonged life of a device is one of the major problems.
The driving voltage of a device greatly depends on a carrier transporting material that transports carriers such as a hole and an electron to an emissive layer. Among them, materials having a carbazole skeleton are known as materials to transport holes (hole transporting materials) (see, for example, Patent Documents 1 and 2). Further, the material having a carbazole skeleton has a high triplet level, and is therefore known as a host material of an emissive layer (see, for example, Patent Document 3).